186 
F. Cavers. 
(Fig. 10, 10-13), the most Alga-like form, colonies of considerable 
size are formed by repeated division within a thick stratified 
gelatinous investment. 
The Noctilucaceae (Cystoflagellata) are probably derived from 
Pyrocystis-Yike Peridiniales. In Noctiluca (Fig. 10, 14) the spherical 
cell shows great resemblance in internal structure to Pyrocystis, 
though there is no cell-wall and there are, on the other hand, some 
elaborations not found in Pyrocystis —e.g., the thick tentacle which 
is transversely striated and shows movements, the short flagellum 
in the gullet-like opening guarded by two projections (“tooth ” and 
“lip”). The reproduction of Noctiluca is a somewhat remarkable 
process—after conjugation of two cells budding occurs, and from 
the buds there arise motile cells which show Gymnodinium-Yike 
features—a transverse groove (without flagellum, however) and on 
the concave ventral side a backwardly directed longitudinal 
flagellum. The other genera of the family— Leptodiscus (Fig. 10, 
15, 16) and Craspedotella (Kofoid, 71)—also show specialised 
structure, and do not serve to fill the gap between Noctiluca and 
Pyrocystis', in Leptodiscus the cell has the form of a watch-glass, 
the convex ventral surface having a wide gullet-like depression on 
one side, and on the other and a narrow pit containing a flagellum, 
while Craspedotella resembles a medusa in form. 
Reference has already been made to a possible connection 
between Gymnodiniaceae and the Infusoria. Certain organisms 
are also known which appear to lead from the Peridiniales to 
another group of Protozoa—the Radiolaria. The flagellated spores 
produced by various Radiolaria (for details and some of Brandt’s 
figures of these, see Gamble’s account of this group in Lankester’s 
Treatise on Zoology, 151) present an extraordinarily close 
resemblance to Gymnodinium and other simple Peridiniales, and 
suggest the origin of this Protozoan group from Gyninodininm-Yt\ie 
ancestors. Moreover, Scluitt has described three genera which 
appear to form direct links between Gymnodiniaceae and simple 
Radiolaria, and which also suggest the possible origin of the 
Diatoms; these genera ( Gymnaster, Monaster, Ampliitolus) have an 
internal skeleton which recalls that of Radiolaria, and the body is 
divided into two portions by an equatorial suture, which in 
Ampliitolus (Fig. 10, 21) and Monaster (Fig. 10, 20) is grooved, 
while in Monaster the resemblance to Peridiniales is enhanced by 
the presence of two flagella inserted in this groove and springing 
laterally from the body. In addition, Borgert has shown that 
certain genera— Distephanus (Fig. 10, 17-19), Mesoscena, Dyctiocha, 
Cannopilus —which had been previously placed in the Radiolaria 
(in the bodies of which they live as commensals, and with which 
they agree in having a siliceous skeleton) are Flagellate forms, for 
which he formed the group Silicoflagellata (see also Lemmermann, 
80, 83); these organisms have a skeleton consisting of transverse 
rings which are either free or joined up by longitudinal spicules to 
form a network, and in the genera named there is a single flagellum 
(Borgert’s new genus Ebria has two flagella), while the protoplasm 
contains numerous yellow chromatophores. The Silicoflagellata 
may have been derived from forms like Monaster, or they may have 
come from Chrysomonadinean ancestors—certain Chrysomonads 
